Buying Socks for Preschoolers.

Go to the store, feel on the back of the sock package for the little slit. Open the sticky slit, take out the sock, and try it on him.

If it fits buy several of that package and if it is the wrong size put the sock back in neatly and then put the sticky seams back together and pick the different size.

Lots of people buy their socks like this.

I buy these for my son and he loves them.

There is usually a 'size' and a chart on the top or back that states, will fit SHOE size...
Your son's size would be the first one 7-8.5 (shoe size 9 - 1)
http://www.kohls.com/kohlsStore/kids/boys47/socksunderwea...

My son is about to turn 4 and he wears a size 11-12 shoe. I buy him socks from baby gap in a size 4-5T and they fit well.

I just got socks for my son at Target - he's also 4 and size 11. Got them in the boy section, I think they were size medium but for the smaller kids. I think the shoe size on it said 9-5 (toddler size 9 to big kid size 5). They fit fine. He likes them :)

Have you seen "Pretty Woman?" At the beginning of the movie, Julia Roberts character is driving his car and talks about your foot being the same size as your arm from your elbow to your wrist. It's true! (I remember seeing people in the theater looking at their arms and down at their shoes.)

If you have him with you, you can try holding the sock up to his arm. Even the socks in the packages often have a picture on them so you can check.

Did you wash the socks in hot water and run them through the dryer? That usually shrinks them quite a bit. If they are still too big, save them for later and buy the next smaller size in the same brand unless you can see that the proportions of that sock brand are not a good match for your son's foot.

If your son is hard to fit, you can try tube socks. But I've been buying Hanes socks for my 2 boys since they were little. One has a super wide foot, the other pretty narrow.